692 HENRY H. DONALDSON 
follow the mean values more regularly; Minnesota, table 5, 
Brandywine, table 7. 
SUMMARY 
From the foregoing discussion, the following conclusions are 
drawn: 
1. - The relative weight of the central nervous system of the 
frog, Rana pipiens, changes during the active season, and such a 
change is probably characteristic for other species of frogs with 
like habits. 
2. The relative weight of the central nervous system is low 
at the time of emergence, high in the midsummer (July) and low 
again at the time of hibernation. During hibernation it remains 
nearly constant. In the formula used to express the weight of 
the central nervous system, the absolute value of C is character- 
istic for the station from which the frogs come. 
3. The range from minimum to maximum in the value of C 
is about 13 per cent, rising 7 per cent from the end of March to 
the end of April, 4 per cent more from the end of April to the end 
of May, and 2 per cent more from the end of May to the first of 
July, remaining stationary in July and then in reverse order falling 
month by month at a similar rate to the end of October. 
4. This variation-in the relative weight according to season is 
due to lack of coincidence between the growth of the central nery- 
ous system and the growth of the entire body. 
5. In frogs from one to four years old, the body weight more 
than doubles during each active season. The precise form of 
the curve representing this body growth is not known. 
6. The growth of the central nervous system is precocious in 
relation to that of the body, but in the absence of direct observa- 
tions on the growth of the body, the form of the curve can only 
be indirectly determined as shown in chart 5. 
7. During the active season, the percentage of water in the 
entire frog falls slightly from spring to summer and rises again 
from summer to autumn. These changes seem to be due to the 
combined effects of advancing age and varying food supply. 
The conclusions just given apply primarily to the interpreta- 
tion of the preceding observations, but secondarily they also 
